The present embodiments relate to a method for adapting the brightness of an X-ray image recorded using a filter, with the filter attenuating, differently in at least two spatial filter regions, the X-ray radiation used for recording the X-ray image. The present embodiments also relate to an X-ray device, a computer program and an electronically readable data medium.
It is known for medical interventions (e.g., minimally invasive interventions) to be performed under X-ray monitoring. In such cases, X-ray images of a recording area, including the intervention area (e.g., the target area), are recorded with an X-ray device continuously and/or cyclically during the intervention and displayed to the at least one person performing the intervention. X-ray images of this type are frequently referred to as fluoroscopic images. Instruments, such as a catheter, used within the scope of the intervention, and/or changes occurring as a result of the intervention may be observed on such X-ray images.
X-ray radiation has an ionizing effect such that a patient and/or other persons involved in the intervention are exposed, during the intervention, to an X-ray dose. The X-ray dose should be kept as low as possible. In order to reduce the X-ray radiation exposure (e.g., for the patient), it has been proposed that a filter is connected downstream of the X-ray source of the X-ray device attenuating the X-ray radiation at least in less relevant portions of the region recorded (e.g., the field of vision of the X-ray device). This is based on the idea that there is frequently only one target region within the region recorded that is relevant for the observer (e.g., a person performing an intervention). Such a target region is frequently referred to as a “region of interest” (ROI), and a corresponding filter may be referred to as an ROI filter. An exemplary design provides that the filter has a central (e.g., circular) filter region in which no attenuation of the X-ray radiation is carried out. This inner filter region is to be directed at the target region (ROI). The inner filter region is surrounded by a further filter region that has a fixed attenuation value such that the filter, in this example, includes a total of two filter regions in which the X-ray radiation is attenuated differently (e.g., not at all in the inner filter region and based on a fixed attenuation value in the outer filter region). Other forms/designs of such an ROI filter are also conceivable (e.g., having other forms of inner filter region and/or a larger number of different filter regions). A filter of this type may be integrated in the housing of the X-ray source and has changeable filter regions (e.g., an inner filter region is movable and/or changeable in size). This makes it possible to reduce drastically overall the X-ray dose that the patient and the other persons in the intervention room are exposed.
An example of an ROI filter of this type is disclosed in U.S. Pat. No. 5,278,887. The filter component there, to be used during fluoroscopy, does not allow for attenuated X-ray radiation for recording a region of interest (ROI) selected by the physician, and a high-intensity low-noise X-ray image is therefore produced. In the regions of the recorded region surrounding the target region, an attenuated radiation is used that provides a less intensive, rather noisy image. Here, between the filter regions (e.g., the inner filter region assigned to the ROI) and the outer filter region having a fixed attenuation value, a transition region may be provided in which the thickness of the filter and/or the attenuation value preferably increase(s) in a linear manner.
Before fluoroscopic X-ray images are displayed to the at least one person performing the intervention and/or are otherwise processed further, the images are usually subjected to image processing (e.g., that accentuates edges, reduces noise and the like). The use of the filter gives rise to an X-ray image that has different brightnesses in the image regions assigned to the different filter regions, and therefore mapping these filter regions presents a problem for some image processing algorithms. Moreover, X-ray images of an even brightness and/or intensity distribution are easier for medical personnel (e.g., persons involved in an intervention) to interpret. It is therefore useful to undertake a brightness adaptation of the X-ray images such that the X-ray images appear as similar as possible in all image regions.
To this end, in U.S. Pat. No. 5,278,887 discusses a real-time image processing system was proposed that averages values of the intensities, ultimately averaging the image values, forming, in the various image regions in order to obtain, based upon these average values, a brightness adaptation through a linear, analytically derived transformation. For transition regions, an approach is proposed that examines the profile within the transition region in a linearized manner. However, this gives rise to a plurality of disadvantages. Due to the fact that the average value is generally formed across all image values in the image regions, no consideration is given to whether and to what extent an average identical image value, therefore an average identical brightness, is expected. Therefore, depending on the anatomy recorded, brightness differences in the image regions may occur. This also applies to the transition regions considered separately. This may lead to X-ray images that are inadequately improved in terms of their quality.
Newer X-ray devices, intended to be used within the scope of medical interventions, often also have functionalities that may automatically adapt the ROI filter (e.g., with regard to the target region (ROI)). To this end, it has been proposed that the viewing direction of a person performing the intervention be determined with the aid of eye tracking technologies and that the location of the ROI, and the position the non-attenuating (e.g., the inner, filter region), be adapted depending on this viewing direction. For example, a proposal of this type is described in US 2012/0187312. Frequently changing filter settings, and the different anatomies located in the focus of attention, further exacerbates the problems with brightness adaptation as proposed by the prior art, as there are constantly different situations arising that result in brightness adaptation of different levels of quality.